1. Field of the Invention
This invention relates to an etherified phenolic chelate resin, to a process for the production of the etherified phenolic chelate resin, and to a method for using the etherified phenolic chelate resin. More specifically, the invention relates to an etherified phenolic chelate resin prepared by stabilizing and protecting the chelate groups of a phenolic chelate resin and converting some or all of the phenolic hydroxyl groups into ether groups; to a process for the production of the etherified phenolic chelate resin; and to a method for adsorptively separating a heavy metal ion from an aqueous solution having a pH of about 7 to about 13 by using the etherified phenolic chelate resin.
2. Description of the Prior Art
Various chelate resins have been used for adsorption, removal and recovery of heavy metal ions. The phenolic chelate resins described in U.S. Pat. Nos. 3,936,399 and 4,024,244 have been widely produced and utilized commercially because they have high hydrophilicity, superior physical and mechanical stability and a high rate of adsorption of heavy metal ions, and then can be regenerated for re-use. Chelate resins of this type which are based on a phenol-aldehyde condensate have the defect of insufficient chemical stability such as alkali resistance, acid resistance, heat resistance and oxidation resistance at high temperatures because of the effect of the phenolic hydroxyl groups.
Purification of brine for production of sodium hydroxide has generally been effected by a flocculation precipitating method based on the addition of alkaline agents. This method comprises adding an alkaline agent to brine to precipitate metals such as calcium, magnesium and iron present in the brine in the form of a difficultly soluble hydroxide or carbonate thereof. In this method, however, the hydroxides or carbonates formed are still soluble to some extent, and the purified brine still inevitably contains about 2 to 30 mg/liter of calcium, about 0.5 to 5 mg/liter of magnesium and about 0.5 mg/liter of iron. (All concentrations are as metals, hereinafter the same.) Removal of such minor amounts of metals requires an apparatus of a large size and large quantities of additives, and is extremely uneconomical.
A method is also known which comprises removing impurities of brine for production of sodium hydroxide using a chelate resin. For example, U.S. Pat. No. 4,060,465 discloses a method for removing impurities in brine for production of sodium hydroxide using a chelate resin whose matrix is a styrene-divinylbenzene copolymer, a styrene-butadiene copolymer, an epichlorohydrin polymer, etc. No disclosure, however, is present in U.S. Pat. No. 4,060,465 as to use of a phenol-type chelate resin.
Japanese Patent Application (OPI) No. 86100/76 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".) discloses a method for electrolyzing purified brine containing less than 0.5 gm/liter of calcium ion, less than 0.1 mg/liter of magnesium ion, and less than 0.3 mg/liter of iron ion obtained by passing brine through a chelate resin (using a styrene/divinylbenzene copolymer as a resin matrix). Japanese Patent Application (OPI) No. 86100/76 is silent on etherified phenolic chelate resins. When brine is purified using a conventional phenolic chelate resin, the chemical stability (e.g., alkali resistance) of the phenolic chelate resin at high temperatures is not sufficient because of the influence of the phenolic hydroxyl groups, and the phenolic chelate resin cannot be regenerated.
Generally, the phenolic hydroxyl groups of a phenol-formaldehyde resin are converted into ether groups by various methods. However, no such conversion has ever been performed on phenolic chelate resins.
The conventional etherification reaction of phenol-formaldehyde resins, as typically shown in U.S. Pat. Nos. 2,625,530 and 2,753,316, for example, comprises converting the phenolic hydroxyl groups into the alkali metal salts thereof using sodium hydroxide or potassium hydroxide, and reacting the alkali metal salt with an equimolar or excessive molar amount, based on the phenolic hydroxyl groups, of an etherifying agent. However, when a phenolic chelate resin is etherified using such a known etherification reaction, the chelate groups will be destroyed because of the high chemical reactivity of the chelate groups. As a result, the resulting chelate resin has reduced adsorptivity, and cannot be used commercially.